There exist a great number of situations in which the pressure of a fluid circulating inside a conduit must be measured without interrupting the circulation of this fluid. One example of such a sensor is described in the international application WO9956614 in the very specific case where the flexible pipe is a vein or an artery.
This known sensor notably includes:
a flexible pipe extending around and along a central axis, this pipe being adapted to contain the fluid the pressure of which must be measured and to be deformed by the effect of the pressure exerted by the fluid, between:                a first deformed position for a first pressure exerted by the fluid, the pipe having in this first position different first and second locations on its periphery the orthogonal projections of which in a plane perpendicular to the central axis are separated by a distance d1, and        a second deformed position for a second pressure exerted by the fluid higher than the first pressure, in the second position the orthogonal projections of the first and second locations in the plane perpendicular to the central axis are separated by a distance d2, the difference between the distances d2 and d1 being at least greater than 0.1 d2,        
a coil the self inductance of which varies as a function of the pressure of the fluid inside the flexible pipe, this coil including at least one turn wound around a winding axis of the coil,
a unit for calculating the pressure of the fluid as a function of the self inductance of the coil.
To be more precise, in this known sensor, a magnetic core fixed to one side of the flexible pipe is used to vary the self inductance of the coil. This magnetic core moves at the same time as the flexible pipe is deformed because of the effect of the pressure of the fluid. It is the movement of this magnetic core relative to the coil that varies the self inductance of the coil and therefore makes it possible to measure the pressure of the fluid inside the flexible pipe. To this end, the winding axis of the coil is parallel to the direction of movement of the magnetic core and therefore perpendicular to the central axis of the flexible pipe. In this known sensor, the coil is rigid and rigidly fixed to the inside of a shell which is itself rigid.
In a relatively similar manner JPH03-131733A and DE102005016812B3 disclose a pressure sensor in which the magnetic core surrounds the flexible pipe. It is then the deformation of the magnetic core by the flexible pipe that causes a variation in the inductance of the coil.
Prior art is also known from U.S. Pat. No. 3,731,184A. In that document the deformation of the flexible pipe varies the area of the cross section of the coil and therefore its self inductance. To this end, the turns of the coil are each formed of a serpentine conductive wire. The manufacture of such a coil is complex.
This known sensor functions correctly. Nevertheless, it is desirable to simplify it to make it simpler to manufacture.